ip routing and manet routing algorithms

Mobile Networks: IP Routing and MANET Routing Algorithms

Wireless Networks and Mobile Systems

By. P. Victer Paul

Dear, We planned to share our eBooks and project/seminar contents for free to all needed friends like u.. To get to know about more free computerscience ebooks and technology advancements in computer science. Please visit....

http://free-computerscience-ebooks.blogspot.com/

http://recent-computer-technology.blogspot.com/

http://computertechnologiesebooks.blogspot.com/

Please to keep provide many eBooks and technology news for FREE. Encourage us by Clicking on the advertisement in these Blog.

http://free-computerscience-ebooks.blogspot.com/

http://recent-computer-technology.blogspot.com/

http://computertechnologiesebooks.blogspot.com/

Mobile Networks: IP Routing and MANET Routing Algorithms 3

Lecture Objectives

● Present the basic principles of routing in general packet-switched networks

● Describe the basic principles of mobile ad hoc networks (MANETs) and MANET routing protocols

● Describe AODV and OLSR as example MANET routing protocols

● Discuss issues related to mobile ad hoc networks and MANET routing protocols


Agenda

● Layer 2 routing● Routing basics

■ Distance vector algorithms■ Link-state algorithms

● Mobile ad hoc networks● Example MANET routing protocols

■ OLSR■ AODV


So far…

● Nodes in a 802.11 basic service set or Bluetooth piconet are directly connected to each other

● There is no need for routing and IP (layer 3) provides essentially no functionality

Ad Hoc Mode

AccessPoint

Infrastructure Mode


Layer 2 Routing (1)

● The source determines that the destination interface is in the same IP subnet■ This necessarily implies that the source and destination are

directly connected by a Layer 2 network

● ARP allows the source to determine the Layer 2 (MAC) address of the destination

● The source encapsulates the IP datagram in a Layer 2 frame, addresses the frame appropriately, and transmits the frame

● Layer 2 “interworking units” (e.g., Ethernet bridges, 802.11 APs) may need to perform some forwarding or routing functions


Layer 2 Routing (2)

Local IP: 10.0.1.4Subnet Mask: 255.255.255.0Local Network: 10.0.1.X

Dest IP = 10.0.1.9(Dest Net = 10.0.1.X)

Local IP: 10.0.1.9

Src

AP

Dest

ARP Requestfor 10.0.1.9

ARPReply

10.0.1.9 Dest

IP MAC

… …


Layer 2 Routing (3)

Local IP: 10.0.1.4Subnet Mask: 255.255.255.0Local Network: 10.0.1.X

Dest IP = 10.0.1.9(Dest Net = 10.0.1.X)

S

AP

D

IP Dest = 10.0.1.9

DA = DBSSID = AP

IP Dest = 10.0.1.9

Dest = D


Need for Layer 3 Routing

● Of course, nodes may not be connected via Layer 2■ Nodes that are in a different IP subnet, i.e., the destination IP

network is different than the local IP network■ Nodes that are out of radio range in an ad hoc wireless

network

● Layer 3, or IP, routing is needed in this case

10.0.1.3

10.0.1.1

10.0.3.3

10.0.3.6

10.4.6.1

10.4.6.9


Routing

● Routing consists of two fundamental steps■ Forwarding packets to the next hop (from an input interface

to an output interface in a traditional wired network)■ Determining how to forward packets (building a routing table

or specifying a route)

● Forwarding packets is easy, but knowing where to forward packets (especially efficiently) is hard■ Reach the destination■ Minimize the number of hops (path length)■ Minimize delay■ Minimize packet loss■ Minimize cost


Routing Decision Point

● Source routing■ Sender determines a route and specifies it in the packet

header■ Supported in IP, although not the typical routing scheme

● Hop-by-hop (datagram) routing■ A routing decision is made at each forwarding point (at each

router)■ Standard routing scheme for IP

● Virtual circuit routing■ Determine and configure a path prior to sending first packet■ Used in ATM (and analogous to voice telephone system)


Routing Table

● A routing table contains information to determine how to forward packets■ Source routing: Routing table is used to determine route to

the destination to be specified in the packet■ Hop-by-hop routing: Routing table is used to determine the

next hop for a given destination■ Virtual circuit routing: Routing table used to determine path

to configure through the network

● A distributed algorithm is required to build the routing table■ Distance vector algorithms■ Link state algorithms


Distance Vector Algorithms (1)

● “Distance” of each link in the network is a metric that is to be minimized■ Each link may have “distance” 1 to minimize hop count■ Algorithm attempts to minimize distance

● The routing table at each node…■ Specifies the next hop for each destination■ Specifies the distance to that destination

● Neighbors can exchange routing table information to find a route (or a better route) to a destination



A

B

C D

BDest Next Metric

B 1C B 2D B 3

ADest Next Metric

A 1C C 1D C 2

ADest Next Metric

B 2B B 1D D 1

ADest Next Metric

C 3B C 2C C 1



● Node A will learn of Node C’s shorter path to Node D and update its routing table

A

B

C D

BDest Next Metric

B 1C C 1D C 2

ADest Next Metric

A 1B B 1D D 1


Link-State Algorithms (1)

● Each node shares its link information so that all nodes can build a map of the full network topology

● Link information is updated when a link changes state (goes up or down)■ Link state determined by sending small “hello” packets to

neighbors

● Given full topology information, a node can determine the next best hop or a route from the source



● Assuming the topology is stable for a sufficiently long period, all nodes will have the same topology information

A

B

C DA-BLink

B-CC-D

A-BLink

B-CC-D

A-BLink

B-CC-D

A-BLink

B-CC-D



● Nodes A and C propagate the existence of link A-C to their neighbors and, eventually, to the entire network

A

B

C D

A-BLink

B-CC-D

A-C

A-BLink

B-CC-D

A-C

A-BLink

B-CC-D

A-C

A-BLink

B-CC-D

A-C

A-C A-C

A-C


MANETs

● A mobile ad hoc network (MANET) is characterized by…■ Multi-hop routing so that nodes not directly connected at

Layer 2 can communicate through Layer 3 routing■ Wireless links■ Mobile nodes

S

D

S

D

LogicalTopology


MANET vs. Traditional Routing (1)

● Every node is potentially a router in a MANET, while most nodes in traditional wired networks do not route packets■ Nodes transmit and receive their own packets and, also,

forward packets for other nodes

● Topologies are dynamic in MANETs due to mobile nodes, but are relatively static in traditional networks

● Routing in MANETs must consider both Layer 3 and Layer 2 information, while traditional protocols rely on Layer 3 information only■ Link layer information can indicate connectivity and

interference



● MANET topologies tend to have many more redundant links than traditional networks

● A MANET “router” typically has a single interface, while a traditional router has an interface for each network to which it connects■ Routed packet sent forward when transmitted, but also sent

to previous transmitter

● Channel properties, including capacity and error rates, are relatively static in traditional networks, but may vary in MANETs



● Interference is an issue in MANETs, but not in traditional networks■ For example, a forwarded packet from B-to-C competes with

new packets sent from A-to-B

● Channels can be asymmetric with some Layer 2 technologies■ Note that the IEEE 802.11 MAC assumes symmetric

channels

● Power efficiency is an issue in MANETs, while it is normally not an issue in traditional networks

● MANETs may have gateways to fixed network, but are typically “stub networks,” while traditional networks can be stub networks or transit networks



● There is limited physical security in a MANET compared to a traditional network■ Increased possibility of eavesdropping, spoofing, and

denial-of-security attacks

● Traditional routing protocols for wired networks do not work well in most MANETs■ MANETs are too dynamic■ Wireless links present problems of interference, limited

capacity, etc.


MANET Routing

● Nodes must determine how to forward packets■ Source routing: Routing decision is made at the sender■ Hop-by-hop routing: Routing decision is made at each

intermediate node

● Difficult to achieve good performance■ Routes change over time due to node mobility■ Best to avoid long delays when first sending packets■ Best to reduce overhead of route discovery and

maintenance■ Want to involve as many nodes as possible – to find better

paths and reduce likelihood of partitions


MANET Routing Approaches

● Decision time■ Proactive or table-driven – maintain routing tables■ Reactive or on-demand – determine routing on an as-needed

basis

● Network structure■ Hierarchical – impose a hierarchy on a collection of nodes

and reflect this hierarchy in the routing algorithm○ May use a proactive protocol for routing within a cluster

or zone○ May use a reactive protocol for routing between

distinguished “cluster heads”■ Non-hierarchical – make decisions among all nodes


Types of MANET Routing

MANET Routing Protocols

Hybrid

Proactive Reactive

Example:OLSR

Example:AODV


Common Features

● MANET routing protocols must…■ Discover a path from source to destination■ Maintain that path (e.g., if an intermediate node moves and

breaks the path)■ Define mechanisms to exchange routing information

● Reactive protocols■ Discover a path when a packet needs to be transmitted and

no known path exists■ Attempt to alter the path when a routing failure occurs

● Proactive protocols■ Find paths, in advance, for all source-pair destinations■ Periodically exchange routing information to maintain paths


IETF MANET Working Group (1)

http://www.ietf.org/html.charters/manet-charter.html

“The purpose of this working group is to standardize IP routing protocol functionality suitable for wireless routing application within both static and dynamic topologies. The fundamental design issues are that the wireless link interfaces have some unique routing interface characteristics and that node topologies within a wireless routing region may experience increased dynamics, due to motion or other factors.”


IETF MANET Working Group (2)

● Currently trying to move four proposed MANET routing protocols to Experimental RFC status■ Ad Hoc On Demand Distance Vector (AODV) protocol■ Dynamic Source Routing (DSR) protocol■ Optimized Link State Routing (OLSR) protocol■ Topology Broadcast based on Reverse-Path Forwarding

(TBRPF) protocol

● URLs■ http://www.ietf.org/html.charters/manet-charter.html■ http://protean.itd.nrl.navy.mil/manet/manet_home.html


OLSR

● Optimized Link State Routing (OLSR) protocol■ On track to become an IETF Experimental RFC

● References■ C. Adjih, et al., “Optimized Link State Routing Protocol,”

IETF Internet Draft, draft-ietf-manet-olsr-08.txt, March 3, 2003.

■ P. Jacquet, P. Muhlethaler, T. Clausen, A. Laouiti, A. Qayyum, and L. Viennot, “Optimized Link State Routing Protocol for Ad Hoc Networks,” Proceedings IEEE INMIC, 2001, pp. 62-68.


OLSR Concepts (1)

● Proactive (table-driven) routing protocol■ A route is available immediately when needed

● Based on the link-state algorithm■ Traditionally, all nodes flood neighbor information in a link-

state protocol, but not in OLSR

● Nodes advertise information only about links with neighbors who are in its multipoint relay selector set ■ Reduces size of control packets

● Reduces flooding by using only multipoint relay nodes to send information in the network■ Reduces number of control packets by reducing duplicate

transmissions


OLSR Concepts (2)

● Does not require reliable transfer, since updates are sent periodically

● Does not need in-order delivery, since sequence numbers are used to prevent out-of-date information from being misinterpreted

● Uses hop-by-hop routing■ Routes are based on dynamic table entries maintained at

intermediate nodes


Multipoint Relays

● Each node N in the network selects a set of neighbor nodes as multipoint relays, MPR(N), that retransmit control packets from N■ Neighbors not in MPR(N) process control packets from N,

but they do not forward the packets

● MPR(N) is selected such that all two-hop neighbors of N are covered by (one-hop neighbors) of MPR(N)

1

4

35

2

6

7

One optimal set for Node 4:MPR(4) = { 3, 6 }

Is there anotheroptimal MPR(4)?


Multipoint Relay Selector Set

● The multipoint relay selector set for Node N, MS(N), is the set of nodes that choose Node N in their multipoint relay set■ Only links N-M, for all M such that NMS(M) will be

advertised in control messages

MS(3) = {…, 4, …}MS(6) = {…, 4, …}

(Assuming bidirectional links)

1

4

35

2

6

7


HELLO Messages (1)

● Each node uses HELLO messages to determine its MPR set

● All nodes periodically broadcast HELLO messages to their one-hop neighbors (bidirectional links)

● HELLO messages are not forwarded

1

4

35

2

6

7

HELLO: NBR(4) = {1,3,5,6}


HELLO Messages (2)

● Using the neighbor list in received HELLO messages, nodes can determine their two-hop neighborhood and an optimal (or near-optimal) MPR set

● A sequence number is associated with this MPR set■ Sequence number is incremented each time a new set is

calculated

1

4

35

2

6

7

At Node 4:NBR(1) = {2}NBR(3) = {2,5}NBR(5) = {3,6}NBR(6) = {5,7}

MPR(4) = {3,6}


HELLO Messages (3)

● Subsequent HELLO messages also indicate neighbors that are in the node’s MPR set

● MPR set is recalculated when a change in theone-hop or two-hop neighborhood is detected

1

4

35

2

6

7

HELLO: NBR(4) = {1,3,5,6}, MPR(4) = {3,6}

MS(6) = {…, 4,…}

MS(3) = {…, 4,…}


TC Messages

● Nodes send topology information in Topology Control (TC) messages■ List of advertised neighbors (link information)■ Sequence number (to prevent use of stale information)

● A node generates TC messages only for those neighbors in its MS set■ Only MPR nodes generate TC messages■ Not all links are advertised

● A nodes processes all received TC messages, but only forwards TC messages if the sender is in its MS set■ Only MPR nodes propagate TC messages


OLSR Example (1)

1

4

35

2

6

7

MPR(1) = { 4 }MPR(2) = { 3 }MPR(3) = { 4 }MPR(4) = { 3, 6 }MPR(5) = { 3, 4, 6 }MPR(6) = { 4 }MPR(7) = { 6 }

MS(1) = { }MS(2) = { }MS(3) = { 2, 4, 5 }MS(4) = { 1, 3, 5, 6 }MS(5) = { }MS(6) = { 4, 5, 7 }MS(7) = { }


OLSR Example (2)

● Node 3 generates a TC message advertising nodes in MS(3) = {2, 4, 5}

● Node 4 forwards Node 3’s TC message sinceNode 3 MS(4) = {1, 3, 5, 6}

● Node 6 forwards TC(3) since Node 4 MS(6)

1

4

35

2

6

7

TC(3) = <2,4,5>


OLSR Example (3)

● Node 4 generates a TC message advertising nodes in MS(4) = {1, 3, 5, 6}

● Nodes 3 and 6 forward TC(4) since Node 4 MS(3) and Node 4 MS(6)

1

4

35

2

6

7

TC(4) = <1,3,5,6>


OLSR Example (4)

● Node 6 generates a TC message advertising nodes in MS(6) = {4, 5, 7}

● Node 4 forwards TC(6) from Node 6 and Node 3 forwards TC(6) from Node 4

● After Nodes 3, 4, and 6 have generated TC messages, all nodes have link-state information to route to any node

1

4

35

2

6

7

TC(6) = <4,5,7>


OLSR Example (5)

● Given TC information, each node forms a topology table

● A routing table is calculated from the topology table

● Note that Link 1-2 is not visible except to Nodes 2 and 3

TC(3) = <2,4,5>

TC(4) = <1,3,5,6>TC(6) = <4,5,7>

1

35

2

6

7

4

Dest Next Hops1 4 22 2 14 4 15 5 16 4 (5) 27 4 (5) 3


AODV

● AODV: Ad hoc On-demand Distance Vector routing protocol■ On track to become an IETF Experimental RFC

● References■ C. E. Perkins, E. M. Belding-Royer, and S. R. Das, “Ad hoc

On-Demand Distance Vector (AODV) Routing,” IETF Internet Draft, draft-ietf-manet-aodv-13.txt, Feb. 17, 2003 (work in progress).

■ C. E. Perkins and E. M. Royer, “Ad hoc On-Demand Distance Vector Routing,” Proceedings 2nd IEEE Workshop on Mobile Computing Systems and Applications, February 1999, pp. 90-100.


AODV Concepts (1)

● Pure on-demand routing protocol■ A node does not perform route discovery or maintenance

until it needs a route to another node or it offers its services as an intermediate node

■ Nodes that are not on active paths do not maintain routing information and do not participate in routing table exchanges

● Uses a broadcast route discovery mechanism● Uses hop-by-hop routing

■ Routes are based on dynamic table entries maintained at intermediate nodes

■ Similar to Dynamic Source Routing (DSR), but DSR uses source routing


AODV Concepts (2)

● Local HELLO messages are used to determine local connectivity■ Can reduce response time to routing requests■ Can trigger updates when necessary

● Sequence numbers are assigned to routes and routing table entries■ Used to supersede stale cached routing entries

● Every node maintains two counters■ Node sequence number■ Broadcast ID


AODV Route Request (1)

● Initiated when a node wants to communicate with another node, but does not have a route to that node

● Source node broadcasts a route request (RREQ) packet to its neighbors

broadcast_id

dest_addr

type flags hopcntresvd

dest_sequence_#

source_addr

source_sequence_#



● Sequence numbers■ Source sequence indicates “freshness” of reverse route to

the source■ Destination sequence number indicates freshness of route

to the destination

● Every neighbor receives the RREQ and either …■ Returns a route reply (RREP) packet, or■ Forwards the RREQ to its neighbors

● (source_addr, broadcast_id) uniquely identifies the RREQ■ broadcast_id is incremented for every RREQ packet sent■ Receivers can identify and discard duplicate RREQ packets



● If a node cannot respond to the RREQ■ The node increments the hop count■ The node saves information to implement a reverse path set

up (AODV assumes symmetrical links)○ Neighbor that sent this RREQ packet○ Destination IP address○ Source IP address○ Broadcast ID○ Source node’s sequence number○ Expiration time for reverse path entry (to enable garbage

collection)


AODV Example (1)

● Node 1 needs to send a data packet to Node 7● Assume Node 6 knows a current route to Node 7● Assume that no other route information exists in the

network (related to Node 7)

1

4

35

2

6

7


AODV Example (2)

● Node 1 sends a RREQ packet to its neighbors■ source_addr = 1■ dest_addr = 7■ broadcast_id = broadcast_id + 1■ source_sequence_# = source_sequence_# + 1■ dest_sequence_# = last dest_sequence_# for Node 7

1

4

35

2

6

7


AODV Example (3)

● Nodes 2 and 4 verify that this is a new RREQ and that the source_sequence_# is not stale with respect to the reverse route to Node 1

● Nodes 2 and 4 forward the RREQ ■ Update source_sequence_# for Node 1■ Increment hop_cnt in the RREQ packet

1

4

35

2

6

7


AODV Example (4)

● RREQ reaches Node 6, which knows a route to 7■ Node 6 must verify that the destination sequence number is

less than or equal to the destination sequence number it has recorded for Node 7

● Nodes 3 and 5 will forward the RREQ packet, but the receivers recognize the packets as duplicates

1

4

35

2

6

7


AODV Route Reply (1)

● If a node receives an RREQ packet and it has a current route to the target destination, then it unicasts a route reply packet (RREP) to the neighbor that sent the RREQ packet

dest_addr

type flags hopcntrsvd

dest_sequence_#

source_addr

lifetime

prsz


AODV Route Reply (2)

● Intermediate nodes propagate the first RREP for the source towards the source using cached reverse route entries

● Other RREP packets are discarded unless…■ dest_sequence_# number is higher than the previous, or■ destination_sequence_# is the same, but hop_cnt is smaller

(i.e., there’s a better path)

● RREP eventually makes it to the source, which can use the neighbor sending the RREP as its next hop for sending to the destination

● Cached reverse routes will timeout in nodes not seeing a RREP packet


AODV Example (5)

● Node 6 knows a route to Node 7 and sends an RREP to Node 4■ source_addr = 1■ dest_addr = 7■ dest_sequence_# = maximum(own sequence number,

dest_sequence_# in RREQ)■ hop_cnt = 1

1

4

35

2

6

7


AODV Example (6)

● Node 4 verifies that this is a new route reply (the case here) or one that has a lower hop count and, if so, propagates the RREP packet to Node 1■ Increments hop_cnt in the RREP packet

1

4

35

2

6

7


AODV Example (7)

● Node 1 now has a route to Node 7 in three hops and can use it immediately to send data packets

● Note that the first data packet that prompted path discovery has been delayed until the first RREP was returned

1

4

35

2

6

7

Dest Next Hops

7 4 3


AODV Route Maintenance

● Route changes can be detected by…■ Failure of periodic HELLO packets■ Failure or disconnect indication from the link level■ Failure of transmission of a packet to the next hop (can

detect by listening for the retransmission if it is not the final destination)

● The upstream (toward the source) node detecting a failure propagates an route error (RERR) packet with a new destination sequence number and a hop count of infinity (unreachable)

● The source (or another node on the path) can rebuild a path by sending a RREQ packet


AODV Example (8)

● Assume that Node 7 moves and link 6-7 breaks● Node 6 issues an RERR packet indicating the broken

path● The RERR propagates back to Node 1● Node 1 can discover a new route

1

4

35

2

6

7

7


Hierarchical Algorithms (1)

● Scalability – MANET protocols often do not perform well for large networks (especially if not dense)■ Global topology is based on the connectivity of each mobile

node

● Clusters can be used to provide scalability■ Clusters are formed (dynamically, of course) to provide

hierarchy■ Global routing is done to clusters ■ Local routing is done to nodes within a cluster■ Clusters of clusters (super-clusters) can be formed to

extend hierarchy■ Similar in principle to IP subnets


Hierarchical Algorithms (2)

● A special node, called the cluster-head, is designated in each cluster■ Responsible for routing data to or from other clusters■ May be a special node, or may be designated through a

clustering algorithm

● Algorithms■ Clustering -- form clusters■ Cluster-head identification -- may be an integral part of the

clustering algorithm■ Routing -- some routing algorithm is still needed

○ Applied at each level of the hierarchy


Hierarchical Algorithm Example

Cluster 1

Cluster 3

Cluster 2


Summary

● Layer 3 routing is needed to extend wireless mobile networks beyond local area networks of directly connected nodes

● Mobile ad hoc networks use multi-hop routing to enable communications in dynamic topologies

● MANET routing is hard to do well – it experiences the problems of both wireless and mobility

● A number of reactive and proactive MANET routing protocols have been proposed

● MANETs are still a niche application and they are relatively immature

ip routing and manet routing algorithms

Technology

ip routing

ip virtual circuit routing

routing table information

packets source routing

basic principles of

ip layer

typical routing scheme

destination ip network